1. Field of the Invention
The present invention relates to a head chip that is mounted on an ink jet recording device applied to, for example, a printer or a facsimile.
2. Description of the Related Art
Conventionally, there is known an ink jet recording device that records characters and images on a medium to be recorded using an ink jet head having a plurality of nozzles for discharging ink. In such an ink jet recording device, the nozzles of the ink jet head are provided in a head holder so as to oppose the medium to be recorded, and this head holder is mounted on a carriage to be scanned in a direction perpendicular to a conveying direction of the medium to be recorded.
A schematic exploded view of an example of a head chip of such an ink jet head is shown in FIG. 12 and a sectional view of main parts of the same is shown in FIG. 13. As shown in FIGS. 12 and 13, a plurality of grooves 102 are provided in parallel with each other in a piezoelectric ceramic plate 101, and each groove 102 is separated by sidewalls 103. An end portion in the longitudinal direction of each groove 102 is extended to an end surface of the piezoelectric ceramic plate 101 and the other end portion is not extended to the other end surface, making the groove 102 to be gradually shallow. In addition, electrodes 105 for applying a driving electric field are formed on surfaces on opening side of both sidewalls 103 in each groove 102 throughout its longitudinal direction.
In addition, a cover plate 107 is joined on the opening side of the grooves 102 of the piezoelectric ceramic plate 101 via adhesive 109. The cover plate 107 includes a common ink chamber 111 to be a recessed portion communicating with the other end portion where each groove 102 is shallow and an ink supply port 112 that is bored from the bottom portion of this common ink chamber 111 in the direction opposite to the grooves 102.
In addition, a nozzle plate 115 is joined to an end surface of the joined body of the piezoelectric ceramic plate 101 and the cover plate 107 in which the grooves 102 are opened, and nozzle openings 117 are formed in the nozzleplate 115 at positions opposing the respective grooves 102.
Further, a wiring substrate 120 is fixed to the surface of the piezoelectric ceramic plate 101 on the other side of the nozzle plate 115 and on the other side of the cover plate 107. Wiring 122 connected to each electrode 105 via bonding wires 121 or the like is formed on the wiring substrate 120, and a driving voltage can be applied to the electrodes 105 via this wiring 122.
In a head chip configured in this way, when each groove 102 is filled with ink from the ink supply port 112 and a predetermined driving electric field is caused to act on the sidewalls 103 on both sides of the predetermined groove 102 via the electrode 105, the sidewalls 103 are deformed to change the capacity inside the predetermined groove 102, whereby the ink in the groove 102 is discharged from the nozzle opening 117.
For example, as shown in FIG. 14, if ink is discharged from the nozzle opening 117 corresponding to a groove 102a, a positive driving voltage is applied to electrodes 105a and 105b in the groove 102a and, at the same time, opposing electrodes 105c and 105d to the respective electrodes are grounded. Consequently, a driving electric field in the direction toward the groove 102a acts on sidewalls 103a and 103b and, if the driving electric field is perpendicular to a direction of polarization of the piezoelectric ceramic plate 101, the sidewalls 103a and 103b are deformed in the direction of the groove 102a by a piezoelectric thickness slip effect and the capacity inside the groove 102a decreases to increase pressure, whereby the ink is discharged from the nozzle opening 117.
In such a head chip, sound pressure is repeatedly reflected and takes a long time to completely attenuate because a degree of sealing a groove is low, although time to be consumed since vibration of sidewalls due to ink discharge is stopped until pressure of ink inside a groove declines to zero to enable discharge of the next ink depends on a length of a groove, a form of a nozzle opening, and the like. Thus, there is a problem in that it is difficult to achieve high speed consecutive discharge, that is, to achieve high speed printing.
In addition, particularly, since time to be consumed until sound pressure attenuates fluctuates significantly due to a form of a nozzle opening, there is a problem in that it is very difficult to control a discharge amount according to the form of a nozzle opening.
Moreover, a chamber consists of a boundary portion communicating with a common ink chamber and a pump portion from a nozzle opening to the boundary portion which is driven for discharging ink, and converging time during which pressure in the chamber attenuates is determined depending on a length of the pump portion, that is, a distance from the nozzle opening to the boundary portion. Thus, there is a problem in that, if the length of the pump is shortened in order to reduce converging time, the ink discharge property is deteriorated and printing is not performed normally.
In view of such circumstances, it is an object of the present invention to provide a head chip which reduces converging time, during which pressure in a chamber attenuates, to achieve high speed printing without deteriorating the ink discharge property and, at the same time, does not cause converging time to fluctuate even if a discharge amount is controlled according to a shape of a nozzle opening.
According to a first aspect of the present invention for solving the above-mentioned object, there is provided a head chip comprising: chambers defined on a substrate, having one-end portions in a longitudinal direction thereof, which communicate with nozzle openings; and electrodes provided on sidewalls of the chambers, in which a driving voltage is applied to the electrodes so that a capacity within the chambers is changed to discharge ink filled in the inside from the nozzle openings,
characterized in that: an ink chamber plate defining a common ink chamber communicating with the chambers is joined on the substrate; the common ink chamber is provided with a partitioning portion for partitioning the chambers and the common ink chamber; and that communicating holes defining a pump length according to a distance from the nozzle openings are provided in the partitioning portion.
According to a second aspect of the present invention, in the first aspect of the invention, a head chip is characterized in that a plurality of the communicating holes are provided at an interval equivalent to the pump length.
According to a third aspect of the present invention, in the first or second aspect of the invention, a head chip is characterized in that the partitioning portion is formed of a separate member.
According to a fourth aspect of the present invention, in any one of the first to third aspects of the invention, a head chip is characterized in that the substrate is formed of a piezoelectric ceramic plate, and the chamber is defined by forming grooves in the piezoelectric ceramic plate and, at the same time, communicates with the common ink chamber at openings on the opposite side of the substrate at one end portion in the longitudinal direction of the chamber.
According to a fifth aspect of the present invention, in any one of the first to third aspects of the invention, a head chip is characterized in that the sidewalls made of piezoelectric ceramic are arranged on the substrate at a predetermined interval to define the chambers between the sidewalls and, at the same time, the common ink chamber is defined on the substrate, and the chambers and the common ink chamber communicate with each other at one end in the longitudinal direction of the chambers.
In the present invention described above, a communicating hole for defining a length of a pump of a chamber is provided, whereby converging time during which pressure in a chamber attenuates can be reduced without deteriorating the ink supply property and the ink discharge property, and high speed printing can be achieved by consecutively discharging ink at a high speed.